The idea is simple – so simple it was already applied elsewhere. The idea is to provide feedback about the quality of the way people brush their teeth. The Brushduino focuses on entertaining kids to keep them brushing at the right place for the right amount of time. Other projects (with many variants) focus specifically on time spent brushing.

I think embedded projects can go an extra mile (provided they are small enough). You can embark a gyroscope and take into account the types and amount of movements you make while brushing your teeth. This way you also have the time you did it anyway. The toothbrush could communicate with a computer to transmit the data. I guess being offline would save some space at the price of direct feedback. This direct feedback could also come in a simplified way, a bit like the Nike+ Fuelband does: it is not an exact measure that you need but merely the fact you brushed vigorously enough and during enough time. The way a gyroscope work should give the space covered – indirectly if you covered every teeth (to be checked). Connection of the toothbrush to a smartphone or a computer could provide the numerical data as well as some social features (as long as you think brushing your teeth can be something shared with your friends).

In terms of design it could look simply like this:

This kind of device will not replace advices given by dentists. But it can help / accompany people during their daily activities.